The primary purpose of an opening statement is to give the jury a brief outline of what evidence counsel expects to introduce at trial. Argument is not allowed. The trial court's determination of what counsel is allowed to say in opening statement will not be overturned absent a finding of abuse of discretion. The opening statement is not evidence, and the judge will so instruct the jury.

It is improper to inject personal opinion into an opening statement. The opening is a "statement" as opposed to the closing, which is an "argument." Thus, the opening should not be argumentative. Counsel should limit the opening to outlining evidence which he or she reasonably believes will be proven at trial. Misrepresentations about what will be proven may result in a mistrial or a reversal of the conviction. It is improper to make prejudicial or derogatory remarks about the other side or the witnesses for the other side.

The prosecutor in a criminal case, and the plaintiff in a civil case, almost always make an opening statement, although there is no requirement that he or she do so. The decision whether to give an opening rests with counsel. No specific requirements are imposed upon opening statements, and a case will not be dismissed on the basis of a weak opening statement except in truly extraordinary circumstances.

Defense counsel may choose to reserve opening until after the other side presents its case-in-chief. As a general rule, defense counsel gives an opening statement before the evidence begins, rather than reserving it until after the other side's case-in-chief, because defense can offset any impression that there is only one side to the case, can show the jury that it is not conceding any of the other side's case, and can counter the effect upon the jury of hearing only the other side's version of the evidence.

It is more common for counsel to waive opening statements in a trial to the court. Even in these trials, however, it is often important to outline the case to the judge and thereby focus the judge's attention on the legal and factual issues counsel feels are important to the case.